Centrifugal pumping devices are rotodynamic pumping devices which use a rotating impeller within a casing for increasing the pressure and flow rate of a fluid within a fluid conveying network. In centrifugal pumps, a fluid is fed, from an upstream piping system, into the pump casing along or near to the rotating axis of the impeller and is accelerated by the impeller, flowing radially or axially outward into a diffuser or volute chamber, which the fluid exits into a downstream piping system. Rotodynamic pumping devices are typically used for large discharge through smaller heads, and several different types of centrifugal pumps are known, which include radial flow pumps, axial flow pumps and mixed flow pumps.
Mixed flow pumps combine the characteristics of radial and axial flow pumps, wherein the fluid is fed, from an upstream piping system, into the pump casing in which it is radially accelerated and lifted and which it exits at an angle, typically of 0 to 90 degrees relative to the axial direction. Mixed flow pumps operate at higher pressures than axial flow pumps, yet output higher discharges than radial flow pumps.
Several different types of impellers are known for use with rotodynamic pumping devices. Open impellers comprise a series of vanes attached to a central hub for mounting on a shaft, without any form of sidewall or shroud. Semi-open impellers incorporate a single shroud at the back of the impeller. Closed impellers incorporate a shroud on either side of the vanes. The type of impeller varies in accordance with the intended use, the pump characteristics, or a combination of both, and may influence the casing design. For instance, a casing for use with radial flow impellers is typically concentric with the impeller, as opposed to the volute-type casings.
Impellers used in centrifugal pumps may be further classified as single-suction or double-suction impellers, depending on the configuration in which liquid enters the eye of the impeller. A single-suction impeller allows liquid to enter the impeller eye from one side only, whereas a double-suction impeller allows liquid to enter the impeller eye from both sides. The double-suction arrangement has the advantage of balancing the end thrust in both respective directions. However, small capacity centrifugal pumps are usually of a single-suction design, which imposes an unbalanced thrust of the shaft thrust bearing that has to be taken into account, as well as unbalanced forces on the pump which may cause vibrations.
An improved design is required for a centrifugal pump with a double-suction impeller, having an easily scalable capacity and which is economical to manufacture.